The Water CycleThe Water Cycle (or hydrological cycle) is the continuous transfer of water between the sea, the land and the atmosphere. It is a continuous cycle with no beginning or end. Water changes state throughout the cycle between liquid, ice and vapour.

The water cycle is driven by the sun. It heats water in rivers, seas and oceans. Water evaporates into the air. Water can be transpired from vegetation through evapotranspiration. Air currents cause the water vapour to rise. As the air cools the water vapour condenses to form clouds. The condensed water falls as precipition in the form of rain, sleet, snow or hailstone. Some of this precipitation is intercepted by buildings and vegetation. Precipition that is not intercepted can then flow over the surface of the earth as surface run-off. This often makes its way to rivers which in turn feeds lakes, seas and oceans. Most run-off infiltrates into the ground. Some is held in storage under the ground whilst other flows through the soils as groundwater flow. Some ground water returns to the surface through springs.